What is it called: Higher denominational notes (Rupees 20 onwards) display the note's denominational value in numerals when held horizontally at eye level.

A latent image is a security feature where the denominational value becomes visible only when the banknote is held horizontally at eye level and viewed at a specific angle. This hidden numeral is printed in a special way that it remains invisible under normal viewing conditions. The other options are different security features - security thread is a embedded metallic strip, watermark is a design visible when held against light, and optically variable ink changes color when tilted.